go for a 500va ups from apc , its d best. u will get it for around 2300/- (not sure) ... and dont connect ur 2 in 1 scanner/printer and speakers to the ups , it wont give u backup then and maynot take the load also.

if u want a more longer backup then go for a 600va ups from the same brand. bt i think 500va is sufficient as u have a low power hungry config but 600va will be even better.